Laterally diffused metal oxide semiconductor (LDMOS) is a commonly used type of high voltage devices and has an easy compatibility with CMOS process. LDMOS is a power device with a dual diffusion structure. Two ion implantation processes are performed in a same source/drain region. The doping ions in a first implantation process are arsenic ions with a higher concentration and the doping ions in a second ion implantation process are boron ions with a lower concentration. A high temperature activation process is performed after the ion implantation processes. Because the diffusion rate of the arsenic ions is greater than that of the boron ions, boron ions may laterally diffuse further below the interface between the gate structure and the substrate, a channel region with a concentration gradient is formed. The channel length of the LDMOS is determined by the difference between the diffusion distances of the two lateral diffusions.
To improve the voltage withstanding performance of the LDMOS, a drift region is disposed between the source region and the drain region. The doping concentration of the drift region is relatively low. Therefore, when a high voltage is applied to the LDMOS, because the resistance of the drift region is relatively high, the component voltage is relatively high. Thus, the LDMOS is able to withstand a sufficiently high voltage.
However, there is a need to improve the voltage withstanding performance of LDMOS. The disclosed methods and semiconductor structures are directed to solve one or more problems set forth above and other problems in the art.